This invention relates to an optical apparatus and more particularly to an optical apparatus having a good response characteristic and being suitable for use as a display apparatus or an optical switch.
As an optical device with an excellent response characteristic, a device utilizing optically functional material such as a ferroelectric liquid crystal device has recently been highlighted. However, any report on an AC-drive optical device of this type has not yet been announced. This is because this type of optically functional material exhibits a specific change in intensity of transmitted (or reflected) light and the intensity of light emitted from an optical device is reversed in magnitude in response to inversion of the polarity of an external field applied to the optically functional material. Under application of voltage in the AC-drive (which, strictly speaking, zeroes the DC component), the intensity of transmitted light (reflected light) is strengthened (or weakened) in response to positive polarity and conversely weakened (or strengthened) in response to negative polarity, so as to be averaged eventually. In other words, the intensity of transmitted light (reflected light) under the application of voltage (intermediate intensity due to the positive and negative polarity responses) becomes almost indistinctive from the intensity in the absence of the applied voltage.
For example, European Patent Application No. 0032362 discloses an optical apparatus utilizing ferroelectric liquid crystal but it is undesirable to drive such a ferroelectric liquid crystal device with DC. This is because an ion flow caused by DC-drive in a liquid crystal layer creates an electrochemical reaction which deteriorates the liquid crystal and in addition, the alignment control layer for aligning liquid crystal molecules is damaged for unknown reasons.
For the reasons set forth above, the advent of a practical optical apparatus has been desired which utilizes optically functional material having such a characteristic that the intensity of light emitted from an optical device changes asymmetrically in response to inversion of the polarity of an applied external field.
An object of this invention is to provide an optical apparatus which can provide high contrast under AC-drive irrespective of the fact that optically functional material used in the apparatus has such a characteristic that the intensity of light emitted from an optical device (radiant light intensity) is reversed in magnitude in response to inversion of the polarity of an external field applied to the optically functional material.